大學英語自學教程 unit 18

[00:00.00]Unit 18 text A [00:04.88]Why Are Maps Drawn with North at the Top ? [00:08.15]為什么地圖繪制得北方在上？ [00:11.42]Now it is hard to visualize a map that does not feature north at the top [00:15.24]現(xiàn)在很難想像一幅不是北方朝上的地圖， [00:19.07]but this was not always so. [00:21.25]但過去的情況并不總是這樣。 [00:23.43]The oldest known map in the accepted sense of the world was drawn about 3,800 BC, [00:28.21]現(xiàn)在被人們認可的最古老的地圖繪制于大約公元前3800年 [00:32.99]and represents the river Euphrates flowing through northern Mesopotamia, Iraq. [00:37.42]圖上顯示幼發(fā)拉底河流經(jīng)伊拉克的美索不達米亞平原北部。 [00:41.85]This,and others that followed it, [00:44.23]這幅地圖以及 [00:46.60]were little more than rough sketches of localized features; [00:49.63]后來的地圖比地方地理特征略圖好不了多少； [00:52.66]it was not until many centuries later that the ancient Greeks placed [00:56.49]直到許多世紀之后，古希臘人 [01:00.32]the science of map--making on a sound footing. [01:03.29]才把地圖繪制學置于可靠的基礎之上。 [01:06.27]At the forefront of the pioneers in the field [01:09.00]在此領域最早的先驅者首推 [01:11.73]was the Greek mathematician philopher Claudius Ptolemaeus (c.AD 90-168), [01:17.02]希臘數(shù)學家和哲學家克勞迪’托勒密烏（約公元90年-168年）。 [01:22.31]more popularly known to history as Ptolemy. [01:25.28]歷史上通常稱他為托勒密。 [01:28.24]The last great scientist of the classical period, [01:31.21]他作為古典時期伯最后一位偉大的科學家 [01:34.17]he was the first to draw a map that was based on all available knowledge, [01:37.75]他第一個畫出以當時所有的知識為基礎的地圖， [01:41.33]rather than guess or imagination. [01:43.61]而不是基于猜測和想象。 [01:45.90]Earlier,the Babylonians had attempted to map the world, [01:49.32]在此之前巴比倫人曾試圖繪制世界地圖， [01:52.74]but they presented it in the form of a flattened disc rather than a sphere, [01:56.43]但他們把地圖繪在扁平盤上， [02:00.11]which was the form adopted by Ptolemy. [02:02.59]而非托勒密所采用的球體上。 [02:05.07]Given the state of knowledge of those times, he got things wrong; [02:08.60]鑒于當時人們的知識狀況，他把事情搞錯了。 [02:12.13]for example,his estimate of China [02:14.61]例如，他對中國 [02:17.09]and the Atlantic Oceanwas far from being accurate. [02:20.17]和大西洋的估計遠非準確。 [02:23.26]Nevertheless,it was a useful effort [02:25.68]可是，這是有用的嘗試。 [02:28.11]and the map remained a work of reference for over a thousand years. [02:31.89]而且該地圖1000多年中一直是人們的參考資料。 [02:35.66]In fact, Christopher Columbus used a version of it [02:38.34]事實上，克里斯托夫’哥倫布在探索新大陸的航行中 [02:41.02]when he set sail in search of the New World-- [02:43.50]曾使用過該地圖的一個版本。 [02:45.98]which caused him some navigational problems, [02:48.62]這給他帶來了許多航海問題， [02:51.26]since Ptolemy had calculated wrongly the size of the Atlantic [02:55.03]因為托勒密錯誤地計算了大西洋的大小， [02:58.81]and was unaware that the Pacific Ocean existed. [03:01.79]并且對太平洋的存在一無所知。 [03:04.76]The really important thing about Ptolemy's map was that north was at the top [03:09.19]托勒密的地圖真正重要的地方是其北方朝上。 [03:13.62]The reason for this was that he decided to orientate the map in the [03:17.69]其原因在于他決定以極星的方向給地圖定向 [03:21.77] direction of the Pole Star since Polaris was the immovable guiding light [03:25.90]因為北極星是那時航海者 [03:30.02]in which the voyagers of that era placed their trust. [03:33.00]所信任的不變的導航燈。 [03:35.98]North at the top remained the accepted arrangement until the early Middle Ages [03:40.16]直到教會勢力開始嚴重干涉科學進步的中世經(jīng)， [03:44.34]when the Church began to interfere seriously with the advance of science. [03:48.17]地圖北方朝上一直是為人們所接受的布局。 [03:51.99]In accordance with the orders of the Church, [03:54.36]按照教會的命令， [03:56.72]maps were still produced in accordance with Ptolemy's principles [04:00.16]地圖仍然按托勒密的原則繪制， [04:03.59]but now Jerusalem was the central feature, [04:06.41]但是必須以耶路撒冷國中心， [04:09.23]as it was held to be the center of the Christian faith [04:12.06]因為耶路撒冷被認為是基督教信仰的中心。 [04:14.88]and east was moved to the top. [04:17.10]于是東方被移到上面。 [04:19.32]These maps are often called "T" Maps because they show only [04:23.14]這些地圖經(jīng)常被稱為“T”形地圖， [04:26.97]three continents--Europe, Asia and Africa--separated by the "T" [04:30.75]因為它們只表現(xiàn)三大洲——歐洲、亞洲和非洲 [04:34.52]formed by the Mediterranean Sea and the River Nile. [04:37.39]被地中海和尼羅河所構成的“T”形所分開。 [04:40.27]From a navigational point of view, they were almost useless. [04:43.83]從航海的觀點看，它們幾乎一無所用。 [04:47.40]More accurate maps began to appear in the 14th century, [04:50.59]隨著貿(mào)易的發(fā)展和對羅盤的日益依賴， [04:53.77]with the spread of trade and increasing reliance on the compass. [04:57.10]更精確的地圖直到14世紀開媽出現(xiàn)。 [05:00.43]Once again, north assumed its rightful place at the top of maps. [05:04.12]北方再一次恢復了其在地圖上方的合理位置。 [05:07.80]Text B [05:10.86]You Have a Choice [05:12.69]你面臨選擇 [05:14.51]Two trains are traveling side by sideand at the same speed along parallel tracks. [05:18.39]兩列火車在平行的軌道上同速并駕齊驅。 [05:22.27]We are seated in one of the trains, [05:24.55]我們坐在其中的一列車上， [05:26.82]and with us we have a special speedometer that measures their relative speed [05:30.04]并且隨身帶了一個特殊的測速表來測量它們的相對速度。 [05:33.27]Since the trains are traveling at the same speedtheir relative speed is zero; [05:37.10]因為這們是同速行駛，它們的相對速度為零； [05:40.92]the speedometer therefore reads "0." [05:43.65]因此，速度表的讀數(shù)是“0“。 [05:46.38]Suddenly the other train seems to start pulling ahead of ours. [05:49.41]突然，另一列火車似乎開始趕到我們這列車的前面去了。 [05:52.44]The speedometer shows a reading of 10 miles per hour. [05:55.27]速度表讀數(shù)為10英里每小時。 [05:58.09]The other train has apparently increased its speed. [06:00.52]這一列車顯然增加了速度。 [06:02.95]But can we be absolutely certain of this increase? [06:05.48]但是我們能夠絕對地肯定這一點嗎？ [06:08.01]If your answer is yes, you are wrong. [06:10.64]如果你的答案為“是”，你就錯了。 [06:13.26]You are wrong because all that we know [06:15.50]你錯了是因為我們知道的 [06:17.73]is that the relative speedbetween the two trains [06:20.36]只不過是兩列車的相對速度 [06:22.98]changed from 0 mph to 10 mph. [06:25.71]從0英里每小時增加到10英里每小時。 [06:28.44]Nothing more. [06:30.03]僅此而已 [06:31.63]This change could have been brought about in one of two ways: [06:34.71]這個變化可以由下列二者之一引起： [06:37.79]1.The other train increased its speed. [06:40.61]1。另一列車加了速度； [06:43.44]2.Our train decreased its speed. [06:46.07]2。我們的列車減慢了速度。 [06:48.71]There are thus two possible explanations [06:50.89]因此，有兩種可能的解釋說明這一速度的變化， [06:53.07]to account for the change in speed we don't know which one is right. [06:56.01]但是我們不知道哪一種是對的。 [06:58.95]Furthermore, regardless of which explanation we choose, [07:01.77]此外，不管我們選擇哪一種解釋， [07:04.59]the end result will be the same: [07:06.57]結果都是一樣的： [07:08.54]the other train will arrive at the station first. [07:10.96]另一列車將先到達車站。 [07:13.37]So it makes no difference whether we say that the other trainincreased its speed [07:16.45]所以我們無論是說另一列車提速了 [07:19.54]or that our train decreased its speed. [07:21.56]還是我們的車減速了都沒有區(qū)別。 [07:23.59]Since both explanations lead to the same result you can choose either one. [07:26.72]既然兩種解釋都帶來相同的結果，你可以任選其一。 [07:29.85]Whenever two things are relative, you can choose either one of them. [07:32.83]每當兩個事物是相對的時候，你都可以任選其一。 [07:35.81]The converse is also true: [07:36.83]反之亦然， [07:37.85]whenever you have a choice between two things that are equally possible [07:40.67]即每當你面臨兩個具有相同可能性的事物時， [07:43.49]then the things are relative. [07:45.57]這兩個事物就是相對的。 [07:47.64]There is no reason, except convenience for choosing one explanation over the other. [07:51.28]除非為了方便，否則沒有什么理由選一舍一。 [07:54.91]The relative speed between the trains remains the same, 10 mph; [07:58.15]兩列火車的相對速度每小時10英里保持不變； [08:01.38]and the end result will be the same. [08:03.51]并且最終結果也將是一樣的。 [08:05.64]Now let's suppose that both trains are at the railroad station [08:08.42]現(xiàn)在我們假設兩列火車都停在車站， [08:11.21]loading and unloading passengers and baggage. [08:13.54]下旅客和裝卸行李。 [08:15.88]A half-hour passes. [08:17.71]半小時過去了。 [08:19.54]As we look at the other train through our window, [08:21.67]當我們從車窗看另一列火車時， [08:23.80]we see that our train seems to start moving, smoothly and slowly. [08:27.02]我們看到自己的車好像開始平穩(wěn)而緩慢地移動。 [08:30.25]For a minute or so, our train seems to travel at a uniform speed. [08:33.63]一分鐘左右以后，我們的火車似乎在勻速行駛。 [08:37.02]Our special speedometer [08:38.99]我們的特殊的速度表 [08:40.96]shows that the relative speed between the two trains is 20 mph. [08:44.38]顯示兩列車的相對速度是20英里每小時。 [08:47.80]But as we look out our window, [08:49.83]但是當我們又往窗外看時， [08:51.85]we suddenly see the last coach of the other train [08:54.49]突然發(fā)現(xiàn)另一列火車的末節(jié)車廂從視野里消失， [08:57.13]disappear from sight and notice the motionless station behind it. [09:00.07]并且看到車站被除數(shù)留在后面一動不動。 [09:03.01]So we are not moving after all. [09:05.03]所以我們根本沒有移動。 [09:07.06]The other train has been moving! [09:08.83]是另一列車在移動！ [09:10.61]This peculiar and often frustrating experienceis an effect of relative motion. [09:13.99]這種奇怪又常令人尷尬的經(jīng)歷是相對運動的結果。 [09:17.37]At the train station we cannot tell whether it was our train [09:20.65]在車站上我們分不清是我們的車 [09:23.93]that changed its speed from 0 mph to 20 mph or whether it was the other train [09:28.16]還是另一列車從0英里每小時 [09:32.40]that changed its speed from 0 mph to 20 mph. [09:35.48]變速為20英里每小時。 [09:38.56]Only after the other train pulled out of the'station could we see that it [09:41.59]只是在另一列火車駛出車站以后， [09:44.62]and not our train, was moving. [09:46.75]我們才發(fā)現(xiàn)并非我們的車在動。 [09:48.88]Now let us again raise the question [09:50.81]現(xiàn)在讓我們再一次提出本文開頭所提出的問題： [09:52.74]that was raised at the beginning of this article [09:54.82]在上述事例中我們 [09:56.90]can we be absolutely certain that the other train did indeed in crease its speed, [10:00.23]能夠絕對肯定是另一列車確實擔速 [10:03.56]and in this case pull out of the station? [10:05.53]并駛出車站了嗎？ [10:07.50]If your answer is yes, then you are wrong again. [10:09.99]如果你回答“是”，你又錯了。 [10:12.47]All we can be certain of [10:14.70]所有我們能肯定的 [10:16.93]is that the relative speed between the two trains changed. [10:19.45]只是兩列車的相對速度改變了。 [10:21.98]These examples illustrate an important principlein the spedal theory of relativity. [10:25.21]這些例子說明了狹義相對論的一項重要原則。 [10:28.45]If A appears to be moving at a steady speed relative to B, [10:31.24]如果A看上去以相對于B穩(wěn)定的速度運動， [10:34.02]we cannot know for sure if it is A that is really moving. [10:36.96]我們并不能確定是否A真的在動。 [10:39.90]Perhaps A is standing still, and B is moving. [10:42.77]也許A靜止不動，而B在動。 [10:45.64]Or perhaps both are moving. [10:47.47]或者也許兩者都在動。 [10:49.30]According to relativity, [10:51.04]根據(jù)相對論， [10:52.77]there is no experiment that can be devised to solve the prolem. [10:55.60]設計不出任何一方一個實驗來解決這個問題， [10:58.42]As there is no way of deciding which of the two objects is moving, [11:01.20]因為無法來判定兩個物體中的哪個在動， [11:03.98]we can choose either one as the moving object. [11:06.41]我們可以選擇任何一個當作運動的物體。 [11:08.84]The reason is that their motion is relative, and relativity, [11:11.92]其原因是在于它們運動是相對的； [11:15.00]as we have seen, means that we have a choice. [11:17.63]而相對性，正如我們所看到的那樣，意味著我們面臨選擇。 [11:20.25]This principle--that if two objects are in uniform motionrelative to each other, [11:23.79]如果兩個物體彼此相對勻速運行， [11:27.33]it is impossible to decide which one's moving and which one is at rest [11:30.31]是不可能判定哪個在動，哪個是靜止的， [11:33.29]applies to all objects moving uniformlyin a straight line through the universe. [11:36.76]這個原則通過適合于所有在宇宙中直線勻速運行的物體。 [11:40.24]In relativity you'll find that whenever you have a choice among [11:43.52]在相對論里，你會發(fā)現(xiàn)每當你在兩種具有相同 [11:46.80]things that are equally possible, [11:48.78]可能性的事物中做出選擇的時候， [11:50.77]you are dealing with relative things. [11:52.95]你都在與相對的事物打交道。 [11:55.13]For example, time, which is measured with clocks and watches, [11:58.85]例如，用鐘和表來測量的時間是相對的， [12:02.57]is relative because it can be shown that there is more than one system of time. [12:05.66]因為可以看出有不只一種時間系統(tǒng)。 [12:08.74]All systems of time are equally possible and you can choose any system you wish. [12:12.37]所有時間系統(tǒng)都具有同樣的可能性，進而你可以任選其一。

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